tcp_window_scaling degrades performance

[Maciej Soltysiak]

Hi

I have been experiencied weird problems with network throughput
lately and I after experimenting with /proc/sys/net/ipv4 knobs
I found that when I have tcp_window_scaling 0 I can
get throughput from a distant server of about 600kB/s (well, 200kB/s
is fast enough)

   # links ftp://ftp.task.gda.pl/ls-lR

When I turn tcp_window_scaling to 1 the transfer starts with 600kB,
then drops nicely to 20kB/s then starts growing again and reaches
about 400kB/s

Anyway It works, but there are some hosts, with which I can't talk to
faster than 800B/s !

This is a Debian SID with vanilla-2.6.7-bk20, but I am having these
problems for a few weeks now.

It might be a TCP kernel issue, but I know that between me and the
other hosts is a checkpoint fw-1 fp3, it may be the cause of problems,
because, well, checkpoint is crazy.

Anyway, I can provide tcpdump, and tcptrace analysis of it and the
state of sysctls if anyone would be willing to help me figure out
what's going on.

Regards,
Maciej


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